In the golf ball manufacturing process, it is common practice to form the cover of the ball using injection molding. A mold comprising a pair of parallel plates containing opposed hemispherical cavities is used to form a spherical cavity within which a golf ball core is suspended by retractable pins. Thermoplastic material is supplied to the cavity along a parting line defined where the hemispherical cavities terminate at the surface of the molding plates. The thermoplastic material surrounds the core to form the cover layer of the ball. Vent pins in the bottom of the hemispherical cavities, i.e. at the poles of the golf ball, allow air to exit the cavity as thermoplastic material is applied thereto. Following evacuation, the vent pins plug the vent openings and form pole dimples on the ball.
Injection molds for forming golf balls are well-known in the patented prior art. The Lavallee et al U.S. Pat. No. 5,122,046, for example, discloses a retractable pin golf ball injection mold wherein the clearance at the parting line is reduced to prevent a flash line from being formed at the equator of the ball when the mold plates are separated to eject a finished ball therefrom. The Lavallee et al U.S. Pat. No. 5,827,548 improves on the earlier Lavallee et al patent by providing a retractable pin golf ball injection mold wherein a cooling circuit is provided in the mold plates to decrease the setting time of the thermoplastic material, and a two-stage ejector mechanism is provided to independently eject excess thermoplastic material from the runners used to supply the material to the cavities and to eject the finished golf ball from the mold cavity.
Most golf ball injection molds of the prior art include a vent pin to allow air to be evacuated from the cavities as thermoplastic material is being supplied thereto to allow even distribution of the thermoplastic material around the golf ball centers. Because the vent pins have a circular cross-sectional configuration, the pole dimples on the ball are always circular. It has not been possible, therefore, with prior golf ball injection molds to form a dimpled golf ball without having circular dimples at the poles. However, owing to the realization of the influence of dimple configurations on ball flight, many golf balls today are formed with non-circular dimples. It is thus desirable to be able to form a golf ball with an injection molded cover layer wherein all of the dimples, including those at the poles of the ball, have a non-circular configuration.
Accordingly, it is a primary object of the present invention to provide a vent mechanism for a golf ball injection mold containing a spherical cavity in which a cover layer is applied to a golf ball core to form a dimpled golf ball. The mold contains a vent passage communicating with the spherical cavity and a vent pin is arranged within the passage. The passage extends from the cavity along a radius of the golf ball through one of the poles thereof. The passage has a non-circular end communicating with the cavity, and the pin is operable between a normal position wherein an end of the pin closes the passage lower end and a retracted position wherein the pin end is arranged within the passage and spaced from the cavity to allow air to enter the passage from the cavity as thermoplastic material is supplied to the cavity to form the cover layer on the ball. The pin end has a non-circular cross-sectional configuration corresponding with that of the passage end so that a dimple formed by the pin at the pole of the golf ball has a non-circular configuration.
According to a further object of the invention, the pin is also operable between an extended position wherein the pin end is arranged within the cavity to eject the golf ball therefrom.
Another object of the invention is to form a golf ball having a cover layer containing all non-circular dimples. The cover layer includes two hemispherical surfaces formed by hemispherical cavities of an injection mold. The hemispherical surfaces are identical and are joined at the equator of the golf ball. Each hemispherical surface includes a plurality of first non-circular dimples formed by projections on the surfaces of the hemispherical cavities and a second non-circular dimple formed at the pole of the golf ball, the pole dimple being formed by a non-circular vent pin of the mold. Preferably, none of the dimples overlap. They may have the same or different configurations and sizes.